THE GEOLOGICAL SECTION OF MICHIGAN 403 



The Kalamazoo section of which there are samples is very inter- 

 esting (but there is always the possibility of misplaced samples), and 

 may mean that this part of the state was out of water at intervals up 

 to the Louisville or Guelph epoch and that after the Clinton there 

 was a minor re-emergence, as at the time of the Richmond Medina 

 beds. The succession is the same, limestone, shale, and red beds, 

 only on a smaller scale. It is also worth noting that the shale is 

 "red" in the Carmen well; Petrolia, also "red rock" occurs just above 

 this slate at South Rockwood (1,285-95 feet deep) near Detroit, and 

 the Strasburg sample on top of the Clinton suggests emergence. 

 Toward the end of the time of the Rochester shale then the shore- 

 line probably passed through Kalamazoo. This is the more interest- 

 ing because just southwest in Illinois^ the Clinton is usually about as 

 thick as in Michigan and is followed by a long break in sedimentation. 

 Thus we may imagine that region emerging at the close of Clinton 

 and staying so until after the Guelph, while Michigan did not emerge 

 at Kalamazoo until after the Rochester shale and then at most during 

 the lower part of the Lockport Guelph time only. 



The peculiar feature of this time seems to be an oscillation or 

 tilting, the Clinton extending more to the south, the Rochester and 

 Niagara opening up to the north, and from the time of the Richmond 

 Medina until after the Rochester shore-lines seem to have been in 

 Michigan, with the continental shield fairly high. (Compare Schu- 

 chert, Pis. 64 to 66.) 



19, 20. Lockport and, Guelph dolomites (Manitoulin) . — The Lock- 

 port and Guelph have different fossils but have never been separated 

 paleontologically in Michigan. The upper limit against the Salina 

 or Monroe is marked only in this way, that the Guelph is peculiarly 

 hard and peculiarly white. One cannot absolutely depend upon the 

 presence or absence of anhydrite as a dividing line. It is convenient 

 at times to separate off the lower, less white and uniform part as 

 Lockport (Louisville). The total thickness of the two at maximum 

 seems fairly persistent and uniform, across the lower part of the 

 state 350 to 270 feet. At the north part of the state it appears to be 

 thicker. The well No. 2 St. Ignace gives just 600 feet, as a Cheboygan. 



Extreme whiteness of the upper part, occasional sand grains 



I Savage, Illinois Survey, Bull. No. 8, 108. 



